We have reported two cases of septic arthritis caused by Pasteurella multocida, the first, septic polyarthritis unrelated to animal contact and the other, septic monarthritis after a cat scratch. Serious infections with this gram-negative bacillus must be treated with intravenous penicillin, ampicillin, or a third-generation cephalosporin; aminoglycosides are not effective. A high index of suspicion is appropriate when there is a history of a recent animal-inflicted wound, though infection may also occur with either nontraumatic animal contact or no recognized animal contact at all.